Semiconducting polymer blends for high temperature organic electronics

ABSTRACT

A composition for use as an electronic material. The composition contains at least one organic semiconducting material, and at least one electrically insulating polymer forming a semiconducting blend wherein the insulating polymer acts as a matrix for the organic semiconducting material resulting in an interpenetrating morphology of the polymer and the semiconductor material. The variation of charge carrier mobility with temperature in the semiconducting blend is less than 20 percent in a temperature range. A method of making a film of an electronic material. The method includes dissolving at least one organic semiconducting material and at least one insulating polymer into an organic solvent in a pre-determined ratio resulting in a semiconducting blend, depositing the blend onto a substrate to form a film comprising an interpenetrating morphology of the at least one insulating polymer and the at least one organic semiconductor material.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present U.S. patent application is a divisional of U.S. patentapplication Ser. No. 16/422,665, filed May 24, 2019, and is related toand claims the priority benefit of U.S. Provisional Patent ApplicationNo. 62/677,648 filed May 29, 2018, the contents of which are herebyincorporated by reference in their entirety into the present disclosure.

STATEMENT REGARDING GOVERNMENT FUNDING

This invention was made with government support under N00014-16-1-2551awarded by the Office of Naval Research. The government has certainrights in the invention.

TECHNICAL FIELD

This disclosure relates to methods and compositions for a class oforganic materials that are suitable for electronic devices, which couldfunction at high temperatures.

BACKGROUND

This section introduces aspects that may help facilitate a betterunderstanding of the disclosure. Accordingly, these statements are to beread in this light and are not to be understood as admissions about whatis or is not prior art.

Organic electronics is increasingly becoming a reality as a new form ofelectronic devices. For electronics that must operate in harshenvironments, specifically at elevated temperatures, novel class ofmaterials are needed. In the ubiquitous inorganics, the electronicfunctionalities decline at high temperatures due to increased carrierdensities, junction leakages, and lowered charge carrier mobility. Toimprove the device performances and lifetimes in these harsh conditions,wide-band gap materials and increased amounts of insulating componentshave been demonstrated. Organic semiconductors present a novel class ofmaterials for electronics that must operate at high temperatures owingto their tunable energy band gaps as well as their uniquethermally-activated charge transport feature. With increasingtemperature, the hoping charge transport is commonly favored in organicsleading to improved performances. However, this thermally-activatedcharge transport becomes hampered by unstable morphologies and disruptedmolecular packing at high temperatures. Despite the increasing demandfor high-temperature electronics, little to none has been reported todate on designing organic materials that can withstand elevatedtemperatures, especially at temperatures above 125° C.

For the forgoing reasons, there is an unmet need for approaches that canlead to organic semiconductors with high-temperature capability that canbe deployed in electronic devices operable at high temperatures.

SUMMARY

A composition for use as an electronic material is disclosed. Thecomposition contains at least one organic semiconducting material, andat least one electrically insulating polymer with a glass transitiontemperature in the range of 120-400° C., forming a semiconducting blendwherein the insulating polymer acts as a host or a matrix for theorganic semiconducting material. The at least one insulating polymer andthe at least one semiconducting material together form aninterpenetrating morphology of the at least one insulating polymer andthe at least one organic semiconductor material. Further, the variationof charge carrier mobility in the semiconducting blend in the electronicmaterial with temperature is less than 20 percent in a temperature rangeof 25 to t° C., where t° C. is less than the glass transitiontemperature of the at least one insulating polymer.

A method of making a film of an electronic material is disclosed. Themethod includes dissolving at least one organic semiconducting materialand at least one insulating polymer into an organic solvent in apre-determined ratio resulting in a semiconducting blend, depositing theblend onto a substrate to form a film, and evaporating the organicsolvent, resulting in a semiconducting film. In the semiconducting filmformed, the at least insulating polymer acts as a matrix for the atleast one organic semiconducting material and the at least oneinsulating polymer and the at least one organic semiconducting materialtogether form an interpenetrating morphology of the at least oneinsulating polymer and the at least one organic semiconductor material.

BRIEF DESCRIPTION OF DRAWINGS

Some of the figures shown herein may include dimensions. Further, someof the figures shown herein may have been created from scaled drawingsor from photographs that are scalable. It is understood that suchdimensions or the relative scaling within a figure are by way ofexample, and not to be construed as limiting.

FIG. 1A shows chemical structures of diketopyrrolopyrrole-thiophene(P1), the semiconducting polymer, and polyvinyl carbazole (PVK) thematrix polymer.

FIG. 1B is a schematic representation of a device structure of athermally-stable OFET based on a binary blend comprising asemiconducting polymer vitrified with a high-T_(g) polymer host. Themicrograph in FIG. 1B represents the atomic force microscope (AFM) phaseimage demonstrating the interpenetrating morphology of thehost-semiconductor blend.

FIG. 1C is a schematic illustration of the blending design with thesemiconducting polymer dispersed within rigid host islands.

FIG. 1D shows measured hole mobilities for OFET devices based on (40P1)/(60 PVK) blends at different temperatures at ambient compared withpure P1.

FIG. 1E shows measured hole mobilities for OFET devices based on (40P1)/(60 PVK) blends at different temperatures inside a nitrogen filledglovebox in comparison with pure P1.

FIG. 2A shows temperature-dependent charge carrier mobility in OFETdevices based on P1 blends containing various ratios of PVK.

FIG. 2B shows AFM phase images of the spin-cast thin films of thepolymer blends with various amounts of PVK added for vitrification.Polymer network interconnects could easily be formed with PVK loadingsbelow 70%. Optimal connectivity was observed when near 60% PVK wasadded.

FIG. 2C shows measured OFET mobilities for devices based on optimizedblending ratios.

FIG. 2D shows UV-Vis absorption spectra of PVK-based blends.

FIG. 2E shows bottom-face phase image of the delaminated film of theoptimized blend revealed persistent interdigitation of semiconductingdomains at the substrate interface. The scale bar is 4 μm.

FIG. 3A shows the hole mobility of OFET devices measured under constantheating at 150° C. comparing the thermal stability of P1 and that ofP1/PVK blend.

FIG. 3B shows the characteristic transfer curve of OFET devices afterbeing heated for 1 hour at ambient.

FIG. 3C shows the changes in I_(on)/I_(off) of OFET devices underheating at 150° C. at ambient

FIG. 3D show the changes in threshold voltage when the OFET devices weresubjected to constant heating at 150° C.

FIG. 4A shows molecular structures of the matrix polymers tested forthermally stability and the corresponding AFM height images revealinginterdigitation morphology in with P1.

FIG. 4B shows hole mobilities of OFET devices based on the P1 blends indifferent host matrices measured in open air.

FIG. 4C shows AFM height images revealing morphology change ofPMMA-based blend films upon heating.

FIG. 4D shows donor-acceptor semiconducting polymers studied forthermally stable OFET devices.

FIG. 4E shows measured temperature-dependent hole mobilities for theselected polymer pairs.

FIG. 5 shows several insulting polymer hosts suitable for makingsemiconducting blends of this disclosure

FIG. 6 shows several organic semiconductors suitable for makingsemiconducting blends of this disclosure.

DETAILED DESCRIPTION

Semiconducting properties are shown to be hampered by elevatedtemperatures both in organic and inorganic materials. Inorganicsemiconductors which commonly possess narrow band-gaps suffer fromuncontrolled thermal doping, and organic counterparts, despite theirwider band-gaps, exhibit unstable morphologies at high temperatures. Inthis disclosure, polymer blends comprising a high-glass transitionmatrix and a conjugated semiconductor designed to yield thermally-stablemorphologies for high-temperature organic thin-films transistors aredescribed. The blending allows for the vitrification of the conjugatedcomponent into interdigitated semiconducting crystalline channelsconfined within the rigid matrix domains. Optimized confinement andminimized vibrational rearrangements could be realized via morphologycontrol. Thin-film transistor devices made thereof exhibited thermallystable hole transport at temperatures as high as 220° C.

One way to achieve thermally-stable morphologies and thermally stabledevice performance, especially in conjugated polymer thin-films, is todesign high-glass transition systems which would not soften at elevatedtemperatures. In experiments leading to this disclosure, asemiconducting polymer blend system of a conjugated polymer, and ahigh-glass transition host matrix are described to demonstratetransistor devices that can retain hole mobility as high as 2.5 cm²/Vsup to 220° C. as illustrated in figures to be described below.

In experiments leading to this disclosure, semiconductor polymersdesignated as P1 (poly(diketopyrrolopyrrole-co-thiophene)), P2(Poly(diketopyrrolopyrrole-co-thienothiophene)) and P3(Poly(isoindigo-co-thiophene)for purposes of this disclosure weresynthesized as reported in literature. The composition and structure ofthese polymers P1, P2 and P3 are described later in this detaileddescription. High-glass transition host matrix materials designated aspoly(N-vinyl carbazole (PVK), polyacenaphthylene (PAC) and Poly(methylmethacrylate) (PMMA) (the chemical names are described later in thisdescription) were purchased from Sigma Aldrich and used as received.Other materials, Polycarbonate (PC), polyetherimide (PEI) and Matrimid5218 (MI) were purchased from PolyK Technologies and used as receivedfor the purpose of this disclosure. All polymers and blends prepared forpurposes of the studies leading to this disclosure were dissolved inchloroform (10 mg/ml) and allowed to stir overnight at 40° C. The filmsfor OFET (Organic Field effect Transistors) devices, X-ray diffraction,and AFM (atomic force microscope) characterization were spin-cast fromthe chloroform solutions (2000 rpm, 1 minute were the spin castingparameters.).

In experiments leading to this disclosure, OFET devices were fabricatedand tested. The procedure used is described below: Si/SiO₂ substrateswith Au electrodes were first cleaned using piranha solution (2 vol. 18Msulfuric acid: 1 vol. 30% hydrogen peroxide), followed by copiousrinsing with water, and then sonicated in isopropanol and acetone forfive minutes in each solvent. The cleaned and dried substrates were thenmodified with a self-assembled monolayer of octadodecyltrichlorosilane.Bottom gate, bottom contact OFET devices were then fabricated byspin-coating at ambient. The fabricated devices were then annealed at220° C. for at least 30 minutes to remove their thermal history inside aN₂ glovebox and allowed to slowly cool to ambient before the electricalmeasurements. Charge carrier mobility measurements were carried outusing Keithley 4200 at ambient and inside the glovebox. OFETperformances were obtained by applying a gate bias from −60 V to 6 V,with the potential gradient between the source and drain contacts keptat −60 V. The OFET channel width and length were kept at 1400 and 50 μm,respectively. The thermal stability was evaluated using in-situtemperature-dependent measurement and a Caikang CK-400 hot plate wasused to regulate the temperature. Prior to each measurement, thetemperature was first allowed to stabilize, and the devices were heatedfor at least 30 minutes at each temperature.

In experiments leading to this disclosure, procedures adopted formorphology and crystallinity analysis of the polymers were as follows:Polymer thin films were spin cast on cleaned and OTS-modified Si/SiO₂substrates. The film thickness was measured to be around 170 nm whenchloroform was used as a solvent. AFM images were taken using CypherAsylum AFM and processed through Gwyddion Software. For the in-situtemperature dependent morphology study, the films were first annealedand allowed to cool. The films were first imaged with the stagetemperature maintained to 25° C. The sample stage temperature was thenincreased to 120° C., the instrument limitation, and the films werere-imaged for comparison. The same samples were further heated to 220°C. in open air and re-imaged. To evaluate the crystallinity stability,the films were first annealed to 220° C. and slowly cooled to ambient.GIXD scans were subsequently taken at corresponding temperatures.

In experiments leading to this disclosure, glass transition measurementswere conducted as follows: DSC measurements were carried out using 4 mgof polymer materials with the heating cycle ranging from −30° C. to 300°C. (20° C./min). The DSC second cycles were used for Tg extraction. Forthe fully conjugated polymer which showed no detectable DSC signal,temperature-dependent UV-Vis measurement were used to extract the glasstransition temperature of the studied semiconducting polymers in theirthin film form as previously reported. Briefly, polymer thin films werespin cast onto cleaned glass substrates from chloroform solutions.In-situ temperature-dependent UV-Vis measurement were carried using aCarry 3000 UV-Vis couple with a cryo-chamber for temperature control.The spectra at different temperature were thus used for Tg extractionusing Python and the computing tools available athttps://github.com/seroot/UV_VIS_TG.

Polycarbazole was selected as the host matrix owing to its high glasstransition temperature and its ability to serve as a host semiconductingpolymer. FIG. 1A shows the composition and structure of semiconductorpolymer P1 and high-glass transition host matrix material PVK. FIG. 1Bis a schematic representation of a device structure of athermally-stable OFET based on a binary blend comprising asemiconducting polymer vitrified with a high-T_(g) polymer host. Theschematic in FIG. 1B shows the polymer insulator-semiconductor blend ofthis disclosure. The micrograph in FIG. 1B represents the atomic forcemicroscope (AFM) phase image demonstrating the interpenetratingmorphology of the host-semiconductor blend. The white areas representthe insulating polymer host while the black areas represent the organicsemiconductor. An Interpenetrating morphology is a polymer blendcomprising two or more types of polymers which are at least partiallyinterlaced but not covalently bonded to each other. The two or morenetworks can be envisioned to be entangled in such a way that they areconcatenated and cannot be pulled apart, but not bonded to each other byany chemical bond.

FIG. 1C is a schematic illustration of the blending design with thesemiconducting polymer dispersed within rigid host islands. Referring toFIG. 1C, the rigid host matrix domains comprise the insulating polymerhost such as PVK while the black the semiconducting channels representthe organic semiconductor such as P1. FIG. 1D shows measured holemotilities for OFET devices based on (40 P1)/(60 PVK) blends atdifferent temperatures at ambient compared with pure P1. The blendsrevealed thermally-stable interdigitated crystalline domains of theconjugated polymer within the matrix domains (FIG. 1C). Thelocally-fixed morphology thus enabled the blends to outperform the puresemiconducting polymer at temperatures above 150° C., both in ambientand inert conditions as shown in FIG. 1D and FIG. 1E.

FIG. 2A shows temperature-dependent charge carrier mobility in OFETdevices based on P1 blends containing various ratios of PVK. FIG. 2Bshows AFM phase images of the spin-cast thin films of the polymer blendswith various amounts of PVK added for vitrification. Polymer networkinterconnects could easily be formed with PVK loadings below 70%.Optimal connectivity was observed when near 60% PVK was added. FIG. 2Cshows measured OFET mobilities for devices based on optimized blendingratios. FIG. 2D shows UV-Vis absorption spectra of PVK-based blends.FIG. 2E shows bottom-face phase image of the delaminated film of theoptimized blend revealed persistent interdigitation of semiconductingdomains at the substrate interface. The scale bar is 4 μm.

To attain the interdigitation of the conjugated polymers within thematrix, the (semiconductor)/(matrix) blending volume of ratio was variedfrom 1/9 to 6/4 to establish interconnected morphology in spin-castfilms (FIGS. 2A and 2B). The optimal blending ratio was found between4/6 and 5/5 blending range. In this range, interconnected domains of P1correlated to thermally-stable charge carrier properties. (FIGS. 2B and2C). At higher loadings of the conjugated polymer in the blend, thematrix showed to be expelled resulting in a phase separation as observedfrom AFM phase images. This blending optimization also translated toimproved long-range crystallization of P1 within the confined channels(FIGS. 2D and 2E).

The thermal stability of the fabricated OFET devices was furtherevaluated from electrical measurements carried out under constantheating at 150° C. for at least 6 hours at ambient. FIG. 3A shows thehole mobility of OFET devices measured under constant heating at 150° C.comparing the thermal stability of P1 and that of P1/PVK blend.Referring to FIG. 3A, it can be seen that unlike the parent P1 under thesame conditions, the devices based on PVK retained the original mobilityup to six hours of heating. Due to the unstable morphologies andrearrangement observed in P1 films, the OFET devices made thereof showeddetrimental charge scattering at higher temperatures leading to lowI_(on)/I_(off) and increased threshold voltages. Conversely, thethermally-stabilized PVK blends showed excellent electrical propertieseven after as long as 6 hours of heating as described in FIGS. 3Bthrough 3D. FIG. 3B Shows the characteristic transfer curve of OFETdevices after being heated for 1 hour at ambient. FIG. 3C. Shows thechanges in I_(on)/I_(off) of OFET devices under heating at 150° C. atambient. FIG. 2D Shows the changes in threshold voltage when the OFETdevices were subjected to constant heating at 150° C.

To probe the role of the matrix host in the thermal stabilized thinfilms, other matrix polymers were selected for comparison.Polyacenaphthalene (PAC, Tg ˜214° C.), and polymethylmethacrylate (PMMA,Tg ˜109° C.), polycarbonate (PC, Tg ˜200° C.), polyetherimide (PEI, Tg˜260° C.), and Matrimid 5218 (MI, Tg ˜320° C.). were selected as highglass-transition matrix polymers. Referring to FIG. 4A, the chemicalstructures of the high glass-transition matrices and morphology ofcorresponding blends with P1 exhibiting interdigitated morphologiesanalogous PVK. Referring to FIG. 4B, Temperature dependent transistoranalysis revealed that the blends of high Tg matrices could yield OFETdevices stable up to 220° C. analogous to PVK. For PMMA, which has amuch lower glass transition compared to other matrices, the devicesbased on it blend with P1 showed a decline in mobility at temperaturesabove 140° C. Referring to FIG. 4C, In situ morphology analysis of PMMAblend films further revealed significant changes once the heatingtemperature reaches the Tg of the matrix polymer. The proposed blendingsystem was then probed on other high-performance donor-acceptor polymersto prove the concept. Referring to FIG. 4D the chemical structures ofdiketopyrrolopyrrole bithiophene-thiophene (P2), isoindigo-thiophene(P3), benzodifurandione-based oligo(p-phenylene vinylene (P4), andpoly-hexylthiophene (P5) as the commonly studied semiconducting polymerstested in this disclosure for thermal stability when blended with highTg matrices. Referring to FIG. 4E, the representative blend pairsshowing hole mobility stability up to 220° C. are shown.

Thus in this disclosure, semiconducting polymer blends able to retaintheir electronic properties at temperatures as high as 220° C. have beendescribed. The blending system contains commonly studied donor-acceptorpolymers with high glass transition temperature matrix as theirvitrification medium. The use PVK as a high-Tg host matrix demonstratedOFETs device performance as high as high as 2.5 cm²/Vs even attemperatures beyond 200° C. with reasonable I_(on)/I_(off) as well asthreshold voltages. These unprecedented high-temperature deviceperformances show promising potential applications of this blendingsystem for high-temperature organic electronics.

Based on the above studies, it is an objective of this disclosure todescribe a composition for use as an electronic material. Thecomposition contains at least one organic semiconducting material and atleast one electrically insulating polymer with a glass transitiontemperature in the range of 120-400° C. The at least one organicsemiconducting material and the at least one insulating polymer form asemiconducting blend wherein the at least one insulating polymer acts asa host or a matrix for the semiconducting material. The at least oneinsulating polymer and the at least one semiconducting material togetherform an interpenetrating morphology of the at least one insulatingpolymer and the at least one organic semiconductor material. Thevariation of charge carrier mobility in such a semiconducting blend withtemperature is less than 20 percent in a temperature range 25° C. to t°C., where t° C. is less than the glass transition temperature of thepolymer host. This result can be seen in the data presented in FIG. 1D.In some embodiments of the electronic material of this disclosure, thesemiconducting material is a conjugated polymer. Non-limiting examplesof a conjugated polymer as a semiconducting material of the compositionsof this disclosure are poly-diketopyrrolopyrrole-thiophenes (P1, P2),poly-isoindigo-thiophenes (P3), benzodifurandione-basedoligo(p-phenylene vinylene) (P4), as well as polythiophenes (P5).Examples of the electrically insulating polymer host of the compositionsof this disclosure include, but not limited to polyvinyl carbazole(PVK), polyacenaphthalene (PAC), polycarbonate (PC), polyetherimide(PEI), and polyimide (MI). In some embodiments of the composition of theelectronic material of this disclosure, the fraction of semiconductormaterial in the semiconducting blend is in the range of 0.05 to 0.8 byweight percent.

It should be recognized that in some embodiments of the electronicmaterial of this disclosure, it is possible to have more than oneinsulating polymer host and more than one organic semiconductor. Forexample, we can have an electronic material with PVK and PAC as hostsand P1 as the organic semiconductor. In such a case PVK and PAC wouldtogether form the host matrix while P1 will act as the interpenetratingorganic semiconductor. Similarly, it is possible to make a blendutilizing PVK as the insulating polymer matrix for, say, two organicsemiconductors P1 and P2. Those skilled in the art will readilyrecognize other variations of combining the insulating polymer hosts andorganic semiconductors. Several insulting polymer hosts suitable formaking semiconducting blends of this disclosure are shown in FIG. 5along with their structures. Also, several organic semiconductorssuitable for making semiconducting blends of this disclosure are shownin FIG. 6 along with their structures.

It is another objective of this disclosure to describe a method ofmaking a film of an electronic material. The method includes dissolvingat least one organic semiconducting material and at least one insulatingpolymer into an organic solvent in a pre-determined ratio resulting in asemiconducting blend, depositing the blend onto a substrate to form afilm, evaporating the organic solvent, resulting in a semiconductingfilm. In the resulting semiconductor film, the at least one insulatingpolymer acts as a matrix for the at least one organic semiconductingmaterial and the at least one insulating polymer and the at least oneorganic semiconducting material together form an interpenetratingmorphology of the insulating polymer and the organic semiconductormaterial.

A non-limiting example of a substrate suitable for this method issilicon wafer. In some embodiments of the method, the film can be anelectronic device. A non-limiting example of such an electronic deviceis a transistor.

While the present disclosure has been described with reference tocertain embodiments, it will be apparent to those of ordinary skill inthe art that other embodiments and implementations are possible that arewithin the scope of the present disclosure without departing from thespirit and scope of the present disclosure.

1. A method of making a film of an electronic material, the methodcomprising: dissolving at least one organic semiconducting material andat least one insulating polymer with a glass transition temperature inthe range of 120-140° C. into an organic solvent in a pre-determinedratio resulting in a semiconducting blend; depositing the blend onto asubstrate to form a film, evaporating the organic solvent, resulting ina semiconducting film, wherein the at least one insulating polymer actsas a matrix for the at least one organic semiconducting material and theat least one insulating polymer and the at least one organicsemiconducting material together form an interpenetrating morphology ofthe at least one insulating polymer and the at least one organicsemiconductor material, and wherein a variation of charge carriermobility in the semiconducting blend with temperature is less than 20percent in a temperature range of 25 to t° C., where t° C. is 100° C. orgreater and less than the glass transition temperature of the at leastone insulating polymer.
 2. The method of claim 1, wherein the at leastone organic semiconducting material is one ofdiketopyrrolopyrrole-thiophenes (P1, P2), poly-isoindigo-thiophenes(P3), benzodifurandione-based oligo(p-phenylene vinylene) (P4), andpolythiophenes (P5).
 3. The method of claim 1, wherein the at least oneinsulating polymer is one of polyvinyl carbazole (PVK),polyacenaphthalene (PAC), polycarbonate (PC), polyetherimide (PEI), andpolyimide (MI).
 4. The method of claim 1, wherein the substrate issilicon wafer.
 5. The method of claim 1, wherein the film is anelectronic device.
 6. The method of claim 5, wherein the electronicdevice is a transistor.